The economic conversion of solar radiant energy into electrical or thermal energy requires a relatively high solar flux impinging on the conversion device. Consequently, there have been numerous attempts to collect the generally diffused sunlight falling on relatively large areas, concentrating it into a small area for more efficient conversion of the radiant energy to a more useful form of energy. In U.S. Pat. No. 4,114,592, for example, there is disclosed a lense type device for collecting solar radiation over a relatively large area and focusing it onto a relatively small area. Lense type devices suffer from the disadvantage that they are expensive and have aberrations that result in lower than optimum efficiency. Another type of solar concentrator employs mirrors such as a parabolic mirror for focusing the incident solar radiation onto a thermal energy collector. U.S. Pat. No. 4,154,219 is exemplary of a system employing a parabolic focusing device. These types of devices suffer from thermal and reradiation losses.
Another type of solar concentrating device consists of a large area of fluorescent material on which solar radiation impinges and as a consequence thereof, the fluorescent material emits radiation which is internally reflected within the collector and directed toward a smaller area where it is optically coupled, for example, to a photovoltaic device. Examples of such devices are given in U.S. Pat. No. 4,149, 902 and U.S. Pat. No. 4,188,238. Among the disadvantages of these devices are the high costs of fluorescent materials and the geometric constraints in coupling the collector with an energy converter.
From the foregoing it is apparent there is a need for new and improved solar energy collection systems.